Discovery in apparatus for cooling a wall surface

ABSTRACT

Apparatus for cooling a device that is exposed to extremely high temperatures (such as might be found, for example, within a blast furnace), characterized by the provision of means defining a helicoidal conduit adjacent the wall of the device. In accordance with an important feature of the invention, the crosssectional area of the helicoidal conduit decreases as it approaches the hottest part of the device, whereby the flow speed of the cooling fluid at this point will be a maximum. In one embodiment, the cooling means comprises a tubular member that is inserted within an annular jacket that surrounds the nozzle means of a blast furnace tuyere. In a second embodiment, the cooling means is adapted for insertion in a blast furnace casing or cooling box to define a circulation passage for the cooling fluid, said passage including a helical outer supply portion arranged concentrically about an inner return portion.

United States Patent Brulhet Feb. 1, 1972 54 DISCOVERY IN APPARATUS FOR 2,735,409 2/1956 Avrin et al ....l22/6.6 COOLING A WALL SURFACE 265,156 9/1882 Sheets ..l22/6.6

[72] lnventor: Paul Brulhet, Nilvange, France primary Camby [73] Assignee: Societe Wendel-Sidelor, Societe Anonyme, Atmmey Lawrence Laubscher ayange 57 ABSTRACT 22 F! d: M 11 1970 l l e ay Apparatus for cooling a device that is exposed to extremely [21] Appl.No.: 36,084 high temperatures (such as might be found, for example, within a blast furnace), characterized by the provision of means defining a helicoidal conduit adjacent the wall of the [30] Foreign Apphcat'on Pnomy Dam device. In accordance with an important feature of the inven- May 14, 1969 France ..69l5586 tion, the cross-sectional area of h h li i l ond it decreases as it approaches the hottest part of the device, 52 us. 01 ..263/44, 1 10/1825, l22/6.6, whereby the flow Speed Ofthe cooling fluid at this Point will be 165/134, 266/41 a maximum. in one embodiment, the cooling means comprises [51 1 1m. (:1. ..F23m 5/08, C2lb 7/16 a tubular member that is inserted Within annulariacke 5s 1 Field or Search ..165/134- 263/44- 266/41- surmunds the means a blast fumace a 12'2/6 110/182 second embodiment, the cooling means is adapted for insertion in a blast furnace casing or cooling box to define a circu- [56] References Cited lation passage for the cooling fluid, said passage including a helical outer supply portion arranged concentrically about an UNITED STATES PATENTS inner return P 3,l75,8l7 3/1965 Smith et al. ..266/41 X 8 Claims, 7 Drawing Figures 4 IL 0- 1 7 l I I I I I 4-- F I lit- PATENTED FEB I I972 SHEU 2 BF "3 DISCOVERY IN APPARATUS FOR COOLING A WALL SURFACE This invention relates to a device for cooling an enclosure subjected to high'tem'pe ratures. More particularly, the present invention relates to means for cooling elongated enclosures, such as blast furnace tuyeres and cooling boxes or cases for blast furnaces.

Blast furnace tuyeres and cooling boxes normally extend into the interior of the blast furnace where a high temperature prevails. The shape and position of these two members thus present similarities, although their functions are different. The tuyeres are slightly conical and serve to conduct the airblast and possibly other injections, whereas the cooling cases have various cross sections, generally rectangular. Tuyeres and cases are traversed by water on their inner surfaces. In both cases, the idea is to cool a high-temperature enclosure.

In traditional installations, these tuyeres are of copper and are subjected to temperatures on the order of l,700-2,000 C., their lifetime being only on the order of 150-300 days. The hot-blast temperatures have been increased in recent years from 700 C. to l,000-1,l00 C., and now the temperatures are heading toward l,300-l,400 C. injections of liquid or gaseous hydrocarbons furthermore tend to increase the temperatures'to which the tuyeres are subjected. The heat flow to be absorbed by the tuyere walls, both on the outside and on the inside, thus becomes greater all the time and this results in more and more of a reduction in the lifetime of the tuyeres which are very expensivemembers.

Finally the progressively increasing productivity of blast furnaces, together with the large increase in their dimensions, make the cost of replacement of the tuyeres quite expensive. it thus appears very important to find means permitting the tuyeres-in spite of the stresses from ever higher temperalures-to have a longer lifetime. For this purpose, a study has been made of the phenomena which occurs during the circulation of water in the tuyeres.

It is known that this water boils when the temperature of the outside wall of the water jacket reaches the boiling temperature of the liquid. Thevapor bubbles that are formed on the wall of the jacket are detached more or less rapidly, depending upon the orientation of the wall, and they are then recondensed within the liquid whose steam tension is on the average less than that created by the conditions prevailing in contact with the wall. These bubbles thus accelerate the speed of the convection currents.

If the heat flow evacuated by the cooling liquid is less than the heat flow absorbed by the enclosure,.the temperature of the wall rises and the steam bubble formation intensity increases. The difficulties which these bubbles encounter in breaking away from the wall become so great that a continuous vapor film is formed over all or a part of the wall surface. This phenomenon is called calefaction." Calefaction causes the deterioration of the heat transfer coefficient and, consequently, it limits the heat flow evacuation capacity of the cooling liquid. This results in a growing augmentation of the temperature of the wall material which can go so far as to cause complete destruction of the wall.

In conventional cooling systems, the presence of the calefaction phenomenon at a point on the enclosure is practically uncontrollable. In effect, the control of the efficiency of the system consists in the measurement of the difference between inlet and outlet temperature of the cooling liquid. Now, this measurement represents only the average of the heating between the liquid in contact with the walls and that part of the liquid which has never been in contact.

In an effort to remedy the bad effects of calefaction which lead to the rapid destruction of tuyeres different arrangements have been proposed. A first proposal was to introduce into the water jacket one or-more plunger tubes, which tubes penetrate rather deeply in order to obtain turbulent circulation at the nose of thetuyere. This arrangement proved to be rather ineffective because the water circulation thus created was unconthe water on the wall as a consequence of the different distance of the walls with respect to the outlet of the plunger tubes. Furthermore, abrupt variations in the passage cross sections created relatively large charge losses.

An attempt was also made to insert into the water jacket cylindrical-conical collar means for producing a concentric circulation in the form of thin layers. Nevertheless, the same difficulty was encountered when it came to obtaining a uniform distribution of speeds. To make the system efiicient, large water flow rates are required which are difficult to obtain as the result of the necessarily small dimensions of the water supply and water outlet tubes. It has also been proposed to execute the pipes by means of a massive cast piece with water circulation in the thickness of the piece. But the great thickness of metal causes a large temperature gradient and, since the piece is cast, the cooling circuit presents rough surfaces which diminish the cooling efficiency.

The primary object of the present invention is to remedy the above-mentioned inconveniences by eliminating the causes producing the calefaction phenomenon, by creating on the wall to be cooled sufficient circulation speeds and by making these speeds uniform and easily controllable in each transversal section of the circuit. More particularly, the invention relates to a cooling boxes or device for an enclosure subjected to high temperatures, for example, blast furnace tuyeres and cooling cases. The invention is characterized by the fact that it involves at least one cooling conduit in a serpentine form against the wall of the enclosure to be cooled from the coldest point up to the hottest point, said conduit being connected to return via a spiral conduit.

The present invention includes one or more of the following features:

a. transverse cross section of the conduits presents a progressively variable area, said area diminishing from the entry of the cooling fluid toward the hottest point of the enclosure and increasing from said point toward the outlet of the cooling fluid;

b. the device is shaped in such a way that the speed of the fine water streams is essentially uniform in each cross section of the cooling conduits;

c. the cross-sectional areas S of the conduits-when they are not circularare practically at all points such that their dimensions satisfy the relation (0.45 h S/P), where P is the perimeter of the section considered and h being its smallest dimension, so as to exclude the circulation in thin laminates;

d. the device is independentof or separate from the enclosure to be cooled and whereby the cooling device can be introllable, and-a great disparity existed between the speeds of serted and withdrawn, as desired;

e. the device is made of any material that is inert with respect to the cooling fluid used;

f. the device is made of a substance or a metal that is electronegative with respect to the metal of the enclosure to be cooled;

g. the device is so shaped as to be introduced into or withdrawn from the double wall of the blast furnace pipe;

h. the device includes grooves on its outer and inner lateral surfaces that cooperate with the inner face of the outside wall of the tuyere to define a first helicoidal conduit and with the inside of the inner face wall of said tuyere to define a second helicoidal conduit, the two above conduits having an inverse pitch, the connection between the two conduits being accomplished in the region of the nose of the tuyere by means of a spiral groove;

i. the device is so shaped as to be capable of being introduced into a blast furnace cooling box or case and withdrawn from it if necessary; and

j. the device presents a groove with a generally helicoidal form on the outside and a drill hole on the inside, a connection in the form of a spiral being provided on the side of the bottom of the cooling case between the generally helicoidal groove and the drill hole.

Other objects and advantages of the invention will become apparent from a study of the following specification when viewed in the light of the accompanying drawing, in which:

FIG. 1 is an axial cross section view of a tuyere equipped with a conventional cooling device;

FIG. 2 is a cross section along IIII in FIG. 1;

FIG. 3 is an axial cross section of a tuyere equipped with a cooling device according to the present invention;

FIG. 4 is a cross section along IV-lV in FIG. 3;

FIG. Sis a cross section along VV in FIG. 3;

FIG. 6 is an axial schematic cross section of a cooling box according to the invention, and

FIG. 7 is a cross section along VII-VII in FIG. 6.

Referring now to FIG. 1, the tuyere is provided with conventional cooling means and includes an outer wall I an inner wall 2, both generally of copper, said walls being connected at the nose end 3 to define a jacket for the circulation of the water.

Walls 1 and 2 are integral with the base portion 4 in which are secured a pair of supply tubes 5. Consequently, a turbulent circulation is produced in the region of the nose, the water following the trajectory of the arrows f and being evacuated through an opening 7.

As indicated earlier, this known device is not at all efficient. While similar known devices (for example, devices with concentric circulation in thin layers, or with internal circulation in the interior of a massive piece with great thickness) have produced better results, nevertheless they are still quite unsatisfactory in operation.

The device according to the present invention as represented in FIG. 3 is placed inside the water jacket. More particularly, the tuyere includes outer and inner walls 1 and 2', respectively, connected by the annular transverse wall defined by nose portion 3 and soldered on the base portion 4'. This base, made of steel or copper, is used for attachment on the jacket or shell 8 of the blast furnace and does not require any major cooling because it is exposed to very little heat. On the other hand, nose 3' and wall 1 are subjected to very high temperatures ranges, the maximum temperature being at the nose portion where the blast comes out into the blast furnace.

Inside the jacket defined by walls I and 2', there is introduced, in accordance with the present invention, a cooling member 9 which cooperates with the inner face of the outside wall I to define a first helicoidal conduit 10 for the cross-sectional area of which diminishes gradually from the base portion to the nose portion. The cooling member 9 cooperates with the inner face of internal wall 2 to define a second helicoidal conduit 11 whose pitch is the inverse of that of the first conduit and whose cross-sectional area diminishes in the same direction as that of the first conduit. The connection between the two conduits is accomplished in the region of the nose by means ofa spiral groove 12 which we can see in FIG. 5. On the other hand, FIGS. 3 and 4 illustrate the pair of water inlets 13 that communicate with the base end of the internal helicoidal groove I1, and the pair of water outlets I4 that communicate with the base end of the outer helicoidal groove 10. The inlets and outlets are separated by the screen or divider 15 formed in the base.

The water enters the base through openings 13 and first of all penetrates into a region 16 constituted between the screen and the inside wall of the base. It thus enters the internal helicoidal groove and progresses up to the nose end of the tuyere. From there, it is conducted by spiral groove 12 up to helicoidal groove 10 in order to reach region 17 between the screen and the outside wall of the base from whence it is evacuated via outlets 14 toward the outside.

We can thus see that the entire surface of walls 1' and 2' is flushed by cooling water. Moreover, the progressive reduction of the cross-sectional area of the outside helicoidal grooves, going toward the nozzle, and the progressive increase in the internal circuit, going back toward the base, results in the fact that the hottest parts are cooled most energetically. Furthermore, the direction of rotation of the cooling water around the longitudinal axis of the pipe is unchanged, which means that conduit pressure losses will be minimized.

It is very important that-in each traverse section of the conduitsthe speeds of the water streams be made practically uniform. If the water streams do not all have the same speed, it is difiicult to know the appearance of calefaction at any point along the outside wall of the water jacket and, consequently, it is difficult to control the calefaction, that is to say, the optimum cooling of the tuyere. In effect, this calefaction can be detected only if we know the temperature rise between the inlet and the output of the cooling liquid. However, if the speeds of the water streams are not all essentially equal at all points in each cross section of the circuit, the temperature which we find at the outlet represents only a temperature included between that of the liquid having been in contact with the outside wall of the water jacket and that of the liquid which has never been in contact with that outside wall. Thus the temperature is not representative of the temperature of the outside wall of the water jacket.

In order to obtain this uniformity of speeds, it has been established, in accordance with the present invention, that at any point on the cooling conduits, the cross-sectional area S and the perimeter P must, with the smallest dimension h of said perimeter, present the relationship (0.45 h S/P). This formula indicates, for example, in the case of the device described above, that-since the cross section of the helicoidal conduits is not circular-there must not exist a section placing the fluid in thin layers which would have the result of creating dead zones on the extremities of said sections. Moreover, by thus obtaining a conduit with a section that is favorable from the hydraulic viewpoint, charge losses are reduced. In practice, it has been found that in the case of a rectangular cross section, the length must not be more than eight times the width.

The water output temperature is representative of the temperature on the inner face surface of the outside wall of the water jacket, and thus the flow rate may be regulated in such a way as to adapt the speeds at any moment to the heat flow to be evacuated, thereby obtaining the exchange of heat by convection while avoiding calefaction. Furthermore, the centrifugal effect due to the helicoidal form of the conduit promotes the separation of the steam bubbles.

The device described above, which in summary is a regulator and, in certain places, an accelerator of circulation, permits simple transformation of conventional tuyeres into tuyeres according to the invention, since it suffices to insert the cooling device into the water jackets of the tuyeres. This device can be made up of different materials, such as metal, rubber, plastics, etc., provided these materials are not deteriorated by the cooling liquid or by the temperatures and the operating pressures. on the other hand, since the device required relatively little pressure to obtain large circulation speeds, one can arrange several tuyeres in series on the same water supply line.

In accordance with another application of the invention, the device can also be applied to blast furnace cooling boxes or cases which are subjected to temperatures that increase as they enter more deeply into the furnace.

Referring now to FIG. 6, the cooling box includes an envelope 18 having the general form of a parallelepiped. This envelope is attached in a manner not shown (for example, by welding) to the shell 19 of a blast furnace. Inside the envelope there is provided a removable cooling means 20 whose outside portions are so shaped as to adapt with a technological minimum clearance to the inside of cooling box 18. This device is attached to the case in a conventional manner to compress O-ring 21 to assure a watertight seal.

The outside surface is so shaped as to presentwhen it is in position in the cooling box-a helicoidal conduit 22 whose cross-sectional area decreases regularly from the entrance at 23 up to the end at the bottom of the cooling box. At the bottom of the case, in the forward face of the device, the end of the cooling means 20 cooperates with the adjacent end wall 18' to define a conduit of spiral form, as indicated at 24 in FIG. 7. Thus, the water successively increases in speed toward i the bottom, is directed inwardly toward the center of the bottom of the cooling box, and isexhausted via a central drill hole 25 whose section grows progressively up to outlet 26.

As we know, cooling boxes are often made of steel. The accelerator described above can be advantageously built of a metal that is electronegative with respect to iron, which assures the cooling box of galvanic protection, thus preventing corrosion by the water on the steel wall. The surface of this wall always remains clean and retains its initial heat transfer qualities.

It has been found that, when the blast furnace temperatures on the side of the bottom of the box are on the order of l,400-l,700 C. and the shell temperature is about 60-80 C., there occurs a rise in the temperature of the cooling water not exceeding l2 C. with a speed of l-2 m./s., and a flow rate of m. per hour, the pressure necessary for the circulation of the water being 0.10 bar. The head of the water supply network makes it possible to arrange up to 12 boxes in series. For the boxes subjected to the highest temperatures, it has been possible to obtain water circulation speeds of 4 m./s. with the total temperature rise not exceeding 14 C.

Although the inside cross section of the device is illustrated in H0. 7 as being circular, it is obvious that other shapes may be provided in conformance with the configuration of the cooling box. The efficiency of the device would obviously be greater if the outside form of the box were circular because the thickness of the envelope would then be uniform.

Likewise, if it is desired to cool enclosures with any shape whatsoever, any number of devices according to the invention may be placed in these enclosures.

It will be apparent to those skilled in the art that various changes and modifications may be made in the apparatus described without deviating from the concepts of the present invention.

What is claimed is: 1. Apparatus for cooling a hollow enclosure having longitudinal and end wall portions the outer surfaces of which are subjected to high temperature, including a separate cooling body (9, defining supply and return conduits for conducting cooling fluid longitudinally of said enclosure, the cross sections of said conduits progressively diminishing from the coolest to the hottest and progressively increasing from the hottest to the coolest wall portions of said'enclosure, respectively, said separate cooling body cooperating with the inner surface of the enclosure longitudinal wall portion to define in one of said supply and return conduits a helicoidal cooling passage; the improvement wherein said separate cooling body contains on a peripheral longitudinal surface thereof a continuous longitudinal groove that cooperates with the adjacent longitudinal wall portion of said enclosure to define said helicoidal cooling passage (10, ll, 22);

said separate cooling body containing on an end surface thereof a spiral groove that cooperates with the adjacent end wall portion of said enclosure to define a spiral cooling passage (12, 24) that connects said supply and return conduits.

2. Apparatus as defined in claim 1, wherein the cross section S at each noncircular location of said cooling passages equals the relation 0.45 h S/P, where P and h are the perimeter and smallest dimension, respectively, of the cross section.

3. Apparatus as defined in claim 1, wherein said grooved separate cooling body is formed of a metallic material that is electronegative relative to the enclosure to be cooled.

4. Apparatus as defined in claim I, wherein said enclosure comprises a hollow cylindrical cooling box (18) closed at one end, said separate cooling body being adapted for insertion within and removal from the chamber defined within said cooling box.

5. Apparatus as defined in claim 4, wherein said separate cooling body contains a central bore defining a central condu it (25), said body containing on its outer periphery a helicoidal groove (22) that cooperates with the adjacent longitudinal wall surface of said cooling box to define said helicoidal cooling passage, said body containing at one end a spiral groove (24) that cooperates with the adjacent end wall of said cooling box to define said spiral cooling passage.

6. Apparatus as defined in claim 1, wherein said enclosure comprises a tuyere including spaced concentric generally cylindrical outer (1') and inner (2) walls, and a transverse wall (3) connected'between said walls at one end to define an annular jacket recess;

said separate cooling body being annular and concentrically arranged within said jacket recess, said body containing on its outer and inner longitudinal peripheries helicoidal grooves (l0, ll) of inverse pitch, respectively, one groove cooperating with the adjacent longitudinal surface of the corresponding cylindrical wall to define said helicoidal cooling passage, the other groove cooperating with the adjacent longitudinal surface of the other cylindrical wall to define a further helicoidal cooling passage;

said separate cooling body containing at one end a spiral groove (12) that cooperates with the adjacent end wall of said enclosure to define said spiral cooling passage, said spiral cooling passage being in communication at each end with said helicoidal cooling passages.

7. Fluid-cooled enclosure means adapted for insertion at one end within a blast furnace or the like, comprising an enclosure (1', 18) having at opposite ends a base end adapted for connection with a fixed support, and a nose end (3', 18') adapted to extend within the blast furnace, respectively, whereby the external longitudinal and nose end wall surfaces of said enclosure are subjected to high temperature, said enclosure body containing a chamber extending longitudinally from said base end toward said nose end;

a separate generally cylindrical cooling body (9, 20) mounted concentrically within said chamber, said cooling body including on its outer longitudinally periphery a continuous helicoidal first groove arranged for cooperation with the adjacent longitudinal wall surface of said chamber to define a helicoidal cooling passage (10, 22), said cooling body including on one end a spiral second groove arranged for cooperation with the adjacent end wall of said chamber to define a radially extending spiral passage (12, 24) in communication at one end with said helicoidal cooling passage;

supply conduit means (16, 23) for supplying cooling fluid to the free end of one of said helicoidal and spiral passages; and

return conduit means l7, 6) connected with the free end of the other of said helicoidal and spiral passages.

8. Apparatus as defined in claim 7, wherein said enclosure is generally tubular and contains a central through passage, wherein said chamber is generally annular to define spaced concentrically arranged outer (1) and inner (2) wall portions of said enclosure, and further wherein said cooling body is annular and concentrically arranged between said inner and outer wall portions, said cooling body including on its inner periphery a continuous helicoidal second groove that cooperates with the adjacent surface of said enclosure inner wall portion to define a further helicoidal cooling passage l l) in communication at one end with the other end of said spiral cooling passage. 

1. Apparatus for cooling a hollow enclosure having longitudinal and end wall portions the outer surfaces of which are subjected to high temperature, including a separate cooling body (9, 20) defining supply and return conduits for conducting cooling fluid longitudinally of said enclosure, the cross sections of said conduits progressively diminishing from the coolest to the hottest and progressively increasing from the hottest to the coolest wall portions of said enclosure, respectively, said separate cooling body cooperating with the inner surface of the enclosure longitudinal wall portion to define in one of said supply and return conduits a helicoidal cooling passage; the improvement wherein said separate cooling body contains on a peripheral longitudinal surface thereof a continuous longitudinal groove that cooperates with the adjacent longitudinal wall portion of said enclosure to define said helicoidal cooling passage (10, 11, 22); said separate cooling body containing on an end surface thereof a spiral groove that cooperates with the adjacent end wall portion of said enclosure to define a spiral cooling passage (12, 24) that connects said supply and return conduits.
 2. Apparatus as defined in claim 1, wherein the cross section S at each noncircular location of said cooling passages equals the relation 0.45 h>S/P, where P and h are the perimeter and smallest dimension, respectively, of the cross section.
 3. Apparatus as defined in claim 1, wherein said grooved separate cooling body is formed of a metallic material that is electronegative relative to the enclosure to be cooled.
 4. Apparatus as defined in claim 1, wherein said enclosure comprises a hollow cylindrical cooling box (18) closed at one end, said separate cooling body being adapted for insertion within and removal from the chamber defined within said cooling box.
 5. Apparatus as defined in claim 4, wherein said separate cooling body contains a central bore defining a central conduit (25), said body containing on its outer periphery a helicoidal groove (22) that cooperates with the adjacent longitudinal wall surface of said cooling box to define said helicoidal cooling passage, said body containing at one end a spiral groove (24) that cooperates with the adjacent end wall of said cooling box to define said spiral cooling passage.
 6. Apparatus as defined in claim 1, wherein said enclosure comprises a tuyere including spaced concentric generally cylindrical outer (1'') and inner (2'') walls, and a transverse wall (3'') connected between said walls at one end to define an annular jacket recess; said separate cooling body being annular and concentrically arranged within said jacket recess, said body containing on its outer and inner longitudinal peripheries helicoidal grooves (10, 11) of inverse pitch, respectively, one groove cooperating with the adjacent longitudinal surface of the corresponding cylindrical wall to define said helicoidal cooling passage, the other groove cooperating with the adjacent longitudinal surface of the other cylindrical wall to define a further helicoidal cooling passage; said separate cooling body containing at one end a spiral groove (12) that cooperates with the adjacent end wall of said enclosure to define said spiral cooling passage, said spiral cooling passage being in communication at each end with said helicoidal cooling passages.
 7. Fluid-cooled enclosure means adapted for insertion at one end within a blast furnace or the like, comprising an enclosure (1'', 18) having at opposite ends a base end adapted for connection with a fixed support, and a nose end (3'', 18'') adapted to extend within the blast furnace, respectively, whereby the external longitudinal and nose end wall surfaces of said enclosure are subjected to high temperature, said enclosure body containing a chamber extending longitudinally from said base end toward said nose end; a separate generally cylindrical cooling body (9, 20) mounted concentrically within said chamber, said cooling body including on its outer longitudinally periphery a continuous helicoidal first groove arranged for cooperation with the adjacent longitudinal wall surface of said chamber to define a helicoidal cooling passage (10, 22), said cooling body including on one end a spiral second groove arranged for cooperation with the adjacent end wall of said chamber to define a radially extending spiral passage (12, 24) in communication at one end with said helicoidal cooling passage; supply conduit means (16, 23) for supplying cooling fluid to the free end of one of said helicoidal and spiral passages; and return conduit means (17, 6) connected with the free end of the other of said helicoidal and spiral passages.
 8. Apparatus as defined in claim 7, wherein said enclosure is generally tubular and contains a central through passage, wherein said chamber is generally annular to define spaced concentrically arranged outer (1'') and inner (2'') wall portions of said enclosure, and further wherein said cooling body is annular and concentrically arranged between said inner and outer wall portions, said cooling body including on its inner periphery a continuous helicoidal second groove that cooperates with the adjacent surface of said enclosure inner wall portion to define a further helicoidal cooling passage (11) in communication at one end with the other end of said spiral cooling passage. 